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Storm Drainage System Research Project Flow Rate thRough RooF DRains


Storm Drainage System Research Project Flow Rate thRough RooF DRains

by Julius Ballanco, Pe, CPD, FasPe

The American Society of Plumbing Engineers Research Foundation conducted research on the flow rates through various manufacturers’ roof drains. The research produced stunning results that verified that the sizing method for storm drainage systems, as required in the plumbing codes, is inaccurate. A new approach to sizing storm drainage systems was developed based on the research test results.


This research project was conducted under the direction, and with funding from, the American Society of Plumbing Engineers Research Foundation, Inc. The Board of Directors of the American Society of Plumbing Engineers Research Foundation is as follows:

President: Julius Ballanco, PE, CPD, FASPE

Vice Presidents: David Anelli William Erickson William Hughes, CPD, FASPE, LEED AP Curtis Ray Jr., CPD Max Weiss Stanley Wolfson

Treasurer: Carol Johnson, CPD, LEED AP

Secretary: Jim Kendzel, MPH, CAE

This research project was co-sponsored by the International Association of Plumbing and Mechanical Officials (IAPMO). The American Society of Plumbing Engineers Research Foundation would like to thank IAPMO for their generous support of this important research project.

This research report was subjected to a peer review prior to publication. The American Society of Plumbing Engineers Research Foundation would like to thank the following individuals who participated in the peer review:

Philip D. Dregger, PE, RRCTechnical Roof Services Inc. (TRS)2339 Stanwell Circle, Suite AConcord, CA 94520-4875

Jerry Teitsma, RRC, CCCARCI Education PO Box 796 Granby, CO 80446

Johann L. Willers, PE, RRC, FRCI, FASCERooftop Systems Engineers, PC316 W. Millbrook RoadRaleigh, NC 27609

Dan ColeTechnical Services SupervisorIAPMO4755 E. Philadelphia St.Ontario, CA 91761

Rand AckroydRand Technical Consulting290 High St.Newburyport, MA 01950

Daniel G. Howell, PE FM Global Engineering Standards 1151 Boston-Providence Turnpike Norwood, Massachusetts 02062

Peter J. Gore Willse, PE, FSFPE, MASCE Vice President - Director of ResearchGlobal Asset Protection ServicesXL Group100 Constitution Plaza, 12th Floor Hartford, CT 06103 Dave Orton Senior Engineer NSF International 789 N. Dixboro Road Ann Arbor, MI 48105

ASPE Research Foundation Board of Directors

Copyright © 2012 by American Society of Plumbing Engineers Research Foundation, Inc.

All rights reserved, including rights of reproduction and use in any form or by any means, including the making of copies by any photographic process, or by any electronic or mechanical device, printed or written or oral, or recording for sound or visual reproduction, or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the publisher.


taBle oF Contents

Introduction ........................................................................................................................................................8

Review of Available Data .................................................................................................................................8

Plumbing Codes ............................................................................................................................................... 9

Other Reference Documents....................................................................................................................... 12

Referenced Standard .................................................................................................................................... 13

Roof Drain Testing ............................................................................................................................................ 13

Preliminary Tests ........................................................................................................................................... 13

Testing at IAPMO R&T Laboratories .......................................................................................................... 13

Figure 1 ..............................................................................................................................................................14

Table 1 Roof Drains Tested By IAPMO R&T Laboratories .....................................................................15

Test Results .....................................................................................................................................................16

Interpretation of Data ..................................................................................................................................... 17

Predictions Prior to Testing......................................................................................................................... 17

Analysis of Testing without Roof Drain .................................................................................................... 17

Table 2-0, Comparison Flow Rates to without a Roof Drain ...............................................................18

Analysis of No-Pipe Connected Roof Drain Test ....................................................................................18

Analysis of Straight Pipe Compared to Pipe with an Offset ................................................................18

Analysis of 2-Inch Roof Drains with Straight Pipe ...................................................................................18

Table 2-1, 2” Roof Drain Test Results ........................................................................................................19

Chart 2-1a, 2” Roof Drain Comparison of Test Results ........................................................................20

Chart 2-1b, 2” Roof Drain Comparison of Test Results ........................................................................20

Table 2-2, 2” Roof Drain Test Results .......................................................................................................21


Chart 2-2b, 2” Roof Drain Comparison of Test Results .......................................................................22

Analysis of 2-Inch Roof Drains with Offset Piping ..................................................................................23

Table 2-3, 2” Roof Drain Test Results ......................................................................................................23

Chart 2-3a, 2” Roof Drain Comparison of Test Results .......................................................................24


Analysis of 3-Inch Roof Drains with Straight Pipe ..................................................................................25




Chart 3-1c, 3” Roof Drain Comparison of Test Results ........................................................................27


Chart 3-2a, 3” Roof Drain Comparison of Test Results .......................................................................28


Chart 3-2c, 3” Roof Drain Comparison of Test Results .......................................................................29

Analysis of 3-Inch Roof Drains with Offset Piping ..................................................................................30





Chart 3-3c, 3” Roof Drain Comparison of Test Results ........................................................................ 32

Analysis of 4-Inch Roof Drains with Straight Pipe ................................................................................... 33

Table 4-1, 4” Roof Drain Test Results ........................................................................................................ 33

Chart 4-1a, 4” Roof Drain Comparison of Test Results.........................................................................34


Chart 4-1c, 4” Roof Drain Comparison of Test Results ......................................................................... 35

Chart 4-1d, 4” Roof Drain Comparison of Test Results ........................................................................ 35


Chart 4-2a, 4” Roof Drain Comparison of Test Results........................................................................ 37

Chart 4-2b, 4” Roof Drain Comparison of Test Results........................................................................ 37


Chart 4-2d, 4” Roof Drain Comparison of Test Results........................................................................38

Analysis of 4-Inch Roof Drains with Offset Piping ................................................................................... 39

Table 4-3, 4” Roof Drain Test Results ....................................................................................................... 39


Chart 4-3b, 4” Roof Drain Comparison of Test Results........................................................................40

Chart 4-3c, 4” Roof Drain Comparison of Test Results .........................................................................41

Chart 4-3d, 4” Roof Drain Comparison of Test Results ........................................................................41

Analysis of Performance of Individual 4-Inch Roof Drains ....................................................................42

Chart 4-4a, 4” Roof Drain Model A-3 ........................................................................................................42

Chart 4-4b, 4” Roof Drain Model B-3 ........................................................................................................43

Chart 4-4c, 4” Roof Drain Model C-3 ........................................................................................................43

Chart 4-4d, 4” Roof Drain Model D-3 ........................................................................................................44

Chart 4-4e, 4” Roof Drain Model E-2 ........................................................................................................44

Chart 4-4f, 4” Roof Drain Model E-3 .........................................................................................................45

Chart 4-4g, 4” Roof Drain Model E-5 ........................................................................................................45

Chart 4-4h, 4” Roof Drain Model E-7 ........................................................................................................46

Chart 4-4i, 4” Roof Drain Model F-2 ..........................................................................................................46

Chart 4-4j, 4” Roof Drain Model F-6 .........................................................................................................47

Chart 4-4k, 4” Roof Drain Model G-3 ........................................................................................................47

Chart 4-4l, 4” Roof Drain Model H-3 .........................................................................................................48

Chart 4-4m, 4” Roof Drain Model I-3 ........................................................................................................48

Chart 4-4n, 4” Roof Drain Model J-3 ........................................................................................................49

Chart 4-4o, 4” Roof Drain Model J-8 .......................................................................................................49

Chart 4-4p, 4” Roof Drain Model J-14 ......................................................................................................50

Analysis of 5-Inch Roof Drains with Straight Pipe .................................................................................... 51

Table 5-1, 5” Roof Drain Test Results ......................................................................................................... 51

Chart 5-1a, 5” Roof Drain Comparison of Test Results .........................................................................52

Chart 5-1b, 5” Roof Drain Comparison of Test Results .........................................................................52




Analysis of 5-Inch Roof Drains with Offset Piping ...................................................................................55





Analysis of 6-Inch Roof Drains with Straight Pipe ................................................................................... 57

Table 6-1, 6” Roof Drain Test Results ........................................................................................................ 57

Chart 6-1a, 6” Roof Drain Comparison of Test Results .........................................................................58

Chart 6-1b, 6” Roof Drain Comparison of Test Results .........................................................................58

Chart 6-1c, 6” Roof Drain Comparison of Test Results .........................................................................59

Chart 6-1d, 6” Roof Drain Comparison of Test Results .........................................................................59



Chart 6-2b, 6” Roof Drain Comparison of Test Results ......................................................................... 61

Chart 6-2c, 6” Roof Drain Comparison of Test Results ......................................................................... 61


Analysis of 6-Inch Roof Drains with Offset Piping ...................................................................................63






Engineering Analysis .......................................................................................................................................66

Table 7, Comparison of Roof Drain Flow Rates to Vertical Drain Capacity .....................................66

Table 8, Comparison of Opening Flow Rates to Maximum Roof Drain Flow Rates ....................... 67

Chart 8-2, 5” Roof Drain Straight Pipe with Open Pipe Included ......................................................68

Pressure Measured in the Piping System ................................................................................................69

Sizing Method Recommendation ...............................................................................................................69

Recommended Change to ASME Standard ............................................................................................. 70

Figure 10 ......................................................................................................................................................... 71

Figure 11 ......................................................................................................................................................... 72

Recommended Change to Plumbing Codes ............................................................................................ 73

Table A, Storm Drain Pipe Sizing ............................................................................................................ 73

Table B, Vertical Gutter Sizing ................................................................................................................. 74

Table C, Horizontal Gutter Sizing ............................................................................................................ 75

Appendix A Test Protocol Developed by ASPE Research Foundation ................................................ 76

Appendix B Test Assembly Photos ...............................................................................................................80

Appendix C Test Results of Roof Drains .....................................................................................................89

Test 0-2, 2” Opening without a Roof Drain .............................................................................................89




Test 0-6, 6” Opening without a Roof Drain ..............................................................................................91

1. Manufacturer A, Model A-1 .......................................................................................................................92

2. Manufacturer A, Model A-2 .....................................................................................................................92

3. Manufacturer A, Model A-3 ..................................................................................................................... 93

4. Manufacturer A, Model A-4 .................................................................................................................... 93


5. Manufacturer A, Model A-5 ............................. 94

6. Manufacturer B, Model B-1............................... 94

7. Manufacturer B, Model B-2 ..............................95

8. Manufacturer B, Model B-3 ..............................95

9. Manufacturer B, Model B-4 .............................96

10. Manufacturer C, Model C-1 .............................96

11. Manufacturer C, Model C-2 ..............................97

12. Manufacturer C, Model C-3 .............................97

13. Manufacturer C, Model C-4 ............................98

14. Manufacturer C, Model C-5 ............................98

15. Manufacturer D, Model D-1 .............................99

16. Manufacturer D, Model D-2 ............................99

17. Manufacturer D, Model D-3 ........................... 100

18. Manufacturer D, Model D-4 ......................... 100

19. Manufacturer E, Model E-1 ..............................101

20. Manufacturer E, Model E-2 ............................101

21. Manufacturer E, Model E-3 ............................102

22. Manufacturer E, Model E-4 ...........................102

23. Manufacturer E, Model E-5 ...........................103

24. Manufacturer E, Model E-6 ..........................103

25. Manufacturer E, Model E-7 .......................... 104

26. Manufacturer E, Model E-8 ......................... 104

27. Manufacturer F, Model F-1 ............................ 105

28. Manufacturer F, Model F-2 ........................... 105


30. Manufacturer F, Model F-4 .......................... 106

31. Manufacturer F, Model F-5.............................107

32. Manufacturer F, Model F-6 ...........................107


34. Manufacturer F, Model F-8 .......................... 108

35. Manufacturer G, Model G-1 .......................... 109

36. Manufacturer G, Model G-2 ......................... 109

37. Manufacturer G, Model G-3 ............................110

38. Manufacturer G, Model G-4 ..........................110

39. Manufacturer H, Model H-1 ............................. 111

40. Manufacturer H, Model H-2 ........................... 111

41. Manufacturer H, Model H-3 ............................ 112

42. Manufacturer H, Model H-4 .......................... 112

43. Manufacturer H, Model H-5 .......................... 113

44. Manufacturer I, Model I-1 ............................... 113

45. Manufacturer I, Model I-2 ..............................114

46. Manufacturer I, Model I-3 ..............................114

47. Manufacturer J, Model J-1 .............................115

48. Manufacturer J, Model J-2 ...........................115

49. Manufacturer J, Model J-3 ............................116


51. Manufacturer J, Model J-5 ............................ 117

52. Manufacturer J, Model J-6 ........................... 117

53. Manufacturer J, Model J-7 ............................118



56. Manufacturer J, Model J-10 ..........................119


58. Manufacturer J, Model J-13 .........................120




intRoDuCtionIt was brought to the attention of the American Society of Plumbing Engineers Research Foundation (ASPE RF) that a number of failures with storm drainage systems had occurred. The types of failures included:

• Collapseofroof • Pipefittingseparating • Hangerpulledfromprestressedconcretefloor/ceiling • Floodingofupper-levelbalconydecks • Fittingcomponentfailure • Floodinginthebuildingonupperfloorsduetopipefailure

Many of these failures resulted in litigation. Of the litigation failures directly identified to ASPE RF, all of the cases were settled. Because of the settlements, the specific cases cannot be identified.

Two of the cases involved testing at SGS U.S. Testing Company (now known as QAI Laboratories Ltd.) in Tulsa, Oklahoma. A mock-up roof assembly was created to test the flow rate through various roof drains. In one set of tests, a 10-inch roof drain was tested to determine the flow rate based on the head height of water ponding around the drain. (ASME A112.6.4 regulates roof drains in 2-inch through 6-inch diameters. It is recognized that the standard does not regulate 10-inch roof drains.) In this particular series of tests, the 10-inch roof drain flowed less water than most plumbing engineers anticipated for a roof drain of this size. This accounted for the ponding around the roof drain, with the eventual collapse of the roof.

The other testing conducted, using the same test assembly, was of 4-inch roof drains. In this series of tests, the flow rate through the roof drain exceeded the anticipated flow as identified in the plumbing codes. While the plumbing codes do not identify the flow rate through a roof drain, they do identify the maximum flow rate through the storm drainage piping connected to the roof drain.

The testing on the 4-inch drain demonstrated that the flow in the storm drainage piping exceeded the flow rates for an open channel flow in the stack and horizontal building drain. The high rate of flow created pressure differentials in the piping system that far exceeded the pressures assumed for a typical storm drainage system.

With a test assembly already created, an opportunity was presented to ASPE RF to test roof drains at SGS U.S. Testing Company to determine the different flow rates through standard roof drains. ASPE RF asked roof drain manufacturers to provide roof drains for this testing. The following manufacturers made available their roof drains for testing:

• Canplas • FroetIndustriesLLC • JayR.SmithManufacturingCo. • JosamCo. • MIFAB • Oatey • SiouxChiefManufacturingCo. • WadeDrains • WattsWaterTechnologies • ZurnEngineeredWaterSolutions

The testing was limited to 2-inch through 6-inch roof drains. The limitation was consistent with the sizes regulated in ASME A112.6.4, which is the standard referenced in the plumbing codes for roof drains.

Review oF availaBle DataPrior to any testing, ASPE RF conducted a review of the available data regarding standard roof drains and the design of storm drainage systems. Siphonic roof drains were not researched or evaluated as part of this study.

None of the manufacturers published data regarding the flow rates through their roof drains. This was not unusual since this is not required in the roof drain standard or in the plumbing codes.


Plumbing CodesThe plumbing codes reviewed were the three model plumbing codes used in the United States—IAPMO Uniform Plumbing Code (UPC), ICC International Plumbing Code (IPC), and PHCC-NA National Standard Plumbing Code (NSPC)—and the National Plumbing Code of Canada (NPCC). All three U.S. model plumbing codes and the Canadian plumbing code have similar requirements for roof drains and the design of storm drainage systems.

The U.S. model plumbing codes require the roof drains to conform to ASME A112.6.4. In addition to the reference to the ASME standard, the UPC specifies requirements for the height of the dome strainer and the opening in the dome strainer. Section 1105.2 reads:

1105.2 Dome or Strainer for General Use. Roof drains and overflow drains, except those draining to hanging gutters, shall be equipped with strainers extending not less than 4 inches (102 mm) above the surface of the roof immediately adjacent to the drain. Strainers shall have a minimum inlet area above the roof level not less than one and one-half times the area of the conductor or leader to which the drain is connected.

The NSPC includes requirements for the dome strainer in Section 13.5.2. The section reads:

13.5.2 Dome Strainers Roof areas shall be drained to roof drains having raised dome strainers with dome-free areas complying with ASMEA112.6.4.Theminimumfreedomeareashallbeoneandone-half(1-1/2)timestheareaofthedrainoutletconnection.

EXCEPTIONS (1) Pitched roofs draining to hanging gutters. (2)Roofareassubjecttopedestrianand/orvehiculartraffic.

All three U.S. model plumbing codes require the storm drainage system to be sized for a storm of 60-minute (one-hour) duration and a 100-year return period. The data for the rainfall rates published in the plumbing codes is consistent with the data from the National Weather Bureau.

The sizing of the storm drainage system is based on the capacity of the piping. The UPC and IPC sizing is based on a stack that is one-third full flow and horizontal piping that is flowing full. The NSPC sizing is based on a stack that is7/24fullflowandhorizontalpipingthatisflowingfull.

Other than the difference in the stack capacity, the sizing is basically the same in the plumbing codes. Both the UPC and IPC have sizing tables for gutters.

The sizing tables in the plumbing codes use the projected roof area for sizing the pipe. The projected roof area is the roof area draining to a particular roof drain and storm drainage pipe. To establish the projected roof area, the rainfall rate is divided by the capacity of the pipe and converted to square footage. For example, if a pipe has a capacity of 110 gallons per minute (gpm) and the rainfall rate is 1 inch of rain per hour, the projected roof area equals 10,588 square feet. (1 inch per square foot per hour equates to 0.6233 gallons per hour and when divided by 60 equals 0.010388 gpm. Dividing 110 gpm by the rainfall rate equals 10,588 square feet, which is rounded up in the plumbing codes to 10,600 square feet.)

The U.S. model plumbing code tables list the projected roof area for various rainfall rates in increments of full inches. If the rainfall rate is a fraction of an inch, the projected roof area is determined by dividing the rainfall rate for 1 inch per hour by the rainfall rate. Using the same 10,600 square feet, divide by 3.1 inches per hour to establish the projected roof area for a storm drainage system in Des Plaines, Illinois. The resulting allowable projected roof area would be 3,419 square feet.

The NPCC has sizing requirements similar to the U.S. model plumbing codes. However, the sizing is based on liters of water on the roof for a 15-minute rainfall. The National Building Code of Canada specifies the rainfall rates. The liters are calculated by the roof area multiplied by the rainfall rate, resulting in cubic meters of water on the roof. Cubic meters are then converted to liters (multiplied by 1,000).

The sizing in the NPCC does not consider the flow rate through the roof drain. The sizing is based on the capacity of the storm drainage piping.


The following UPC sizing tables are shown to identify the typical method of sizing in the plumbing codes. The sizing tables from the UPC are reprinted with permission.

uPC taBle 1101.7

siZing oF hoRiZontal RainwateR PiPing

siZe oF PiPe

(inches)

Flow

(gpm at 1/8 inch per foot slope)

MaXiMuM allowaBle hoRiZontal PRoJeCteD RooF aReas

at vaRious RainFall Rates

(square feet)

1(in/h) 2(in/h) 3(in/h) 4(in/h) 5(in/h) 6(in/h)

3 34 3,288 1,644 1,096 822 657 548

4 78 7,520 3,760 2,506 1,880 1,504 1,253

5 139 13,360 6,680 4,453 3,340 2,672 2,227

6 222 21,400 10,700 7,133 5,350 4,280 3,566

8 478 46,000 23,000 15,330 11,500 9,200 7,670

10 860 82,800 41,400 27,600 20,700 16,580 13,800

12 1,384 133,200 66,600 44,400 33,300 26,650 22,200

15 2,473 238,000 119,000 79,333 59,500 47,600 39,650

siZe oF PiPe

(inches)

Flow




(square feet)


3 48 4,640 2,320 1,546 1,160 928 773

4 110 10,600 5,300 3,533 2,650 2,120 1,766

5 196 18,880 9,440 6,293 4,720 3,776 3,146

6 314 30,200 15,100 10,066 7,550 6,040 5,033

8 677 65,200 32,600 21,733 16,300 13,040 10,866

10 1,214 116,800 58,400 38,950 29,200 23,350 19,450

12 1,953 188,000 94,000 62,600 47,000 37,600 31,350

15 3,491 336,000 168,000 112,000 84,000 67,250 56,000

siZe oF PiPe

(inches)

Flow




(square feet)


3 68 6,576 3,288 2,192 1,644 1,310 1,096

4 156 15,040 7,520 5,010 3,760 3,010 2,500

5 278 26,720 13,360 8,900 6,680 5,320 4,450

6 445 42,800 21,400 14,267 10,700 8,580 7,140

8 956 92,000 46,000 30,650 23,000 18,400 15,320

10 1,721 165,600 82,800 55,200 41,400 33,150 27,600

12 2,768 266,400 133,200 88,800 66,600 53,200 44,400

15 4,946 476,000 238,000 158,700 119,000 95,200 79,300


uPC taBle 1101.11

siZing oF RooF DRains, leaDeRs, anD veRtiCal RainwateR PiPing

siZe oF PiPe

leaDeR

oR PiPe (inches)

Flow (gpm)



(square feet)

1

(in/h)2

(in/h)3

(in/h)4

(in/h)5

(in/h)6

(in/h)7

(in/h)8

(in/h)9

(in/h)10

(in/h)11

(in/h)12

(in/h)

2 30 2,880 1,440 960 720 575 480 410 360 320 290 260 240

3 92 8,800 4,400 2,930 2,200 1,760 1,470 1,260 1,100 980 880 800 730

4 192 18,400 9,200 6,130 4,600 3,680 3,070 2,630 2,300 2,045 1,840 1,675 1,530

5 360 34,600 17,300 11,530 8,650 6,920 5,765 4,945 4,325 3,845 3,460 3,145 2,880

6 563 54,000 27,000 17,995 13,500 10,800 9,000 7,715 6,750 6,000 5,400 4,910 4,500

8 1,208 116,000 58,000 38,660 29,000 23,200 19,315 16,570 14,500 12,890 11,600 10,545 9,600

The UPC tables provide a column identifying the flow rate for the pipe. The NSPC also lists the flow rates for each given pipe size. The IPC sizing tables do not list the flow rate for the pipe. However, the flow rate can be derived through calculation. The resulting flow rate would be similar to the UPC.

The flow rates for leaders and vertical drains listed in the NSPC are lower than those in the UPC and IPC since theyarebasedonacapacityof7/24full,asopposedtoone-thirdfullintheUPCandIPC.Thestacksizingintheplumbing codes is based on the stack equation. The stack equation for cast iron pipe is:

Q = 27.88r5/3d8/3

Where: Q = capacity, gpm r = ratio of cross-section area of sheet of water to cross-section area of the stack d = diameter of stack, inches

When calculating the flow rate with a stack capacity of one-third full, the values vary slightly from the values in the UPC and IPC. It is not known when and why the values differed from the calculated values when using the stack equation.

The sizing of the horizontal drains in all of the plumbing codes is based on a calculation using the Manning equation, or Manning expression. The Manning equation is:

V =1.486 R2/3S1/2

n

Where: V = velocity of flow, feet per second n = coefficient of roughness R = hydraulic radius, feet S = hydraulic slope of surface of flow, feet per feet

The equation is also written as:

Q =666.9A R2/3S1/2

n

Where:Q = flow rate, gpmA = area, square feetn = coefficient of roughnessR = hydraulic radius, feetS = hydraulic slope of surface of flow, feet per feet


One of the defining factors when using the Manning equation is the “n” factor, which is the coefficient of roughness. When plumbing codes were first being developed, the “n” factor for piping was assigned a value of 0.015. This is considered fairly rough pipe. As a result, the plumbing codes use a value for sizing horizontal drains of fairly rough pipe.

Studies conducted within the last 50 years have determined that an “n” factor of 0.015 is unrealistic for modern piping materials. The roughest pipe is considered to be cast iron. The “n” factor that is used for cast iron in ASPE’s Plumbing Engineering and Design Handbook of Tables is 0.012. If this factor was applied to the plumbing codes, the flow rate would increase by 25 percent.

The smoothest piping materials are considered to be copper tube, PVC, and ABS. The roughness factor used in the Plumbing Engineering and Design Handbook of Tables for these materials is 0.010. This would increase the flow rate in the plumbing codes by 50 percent.

All of the plumbing codes require a secondary or emergency roof drainage system. A secondary storm drainage system is also required by the ICC International Building Code (IBC). The requirements for a secondary roof drainage system were added to all of the plumbing codes in the 1990s. The change was based on the requirements in ASCE 7, Minimum Design Loads for Buildings and Other Structures. This standard requires roof loads to be based on the maximum amount of ponding on the roof with the primary roof drainage means blocked. If a secondary roof drain is not provided, the loading is based on the height of water to the top of the parapet.

While the plumbing codes added requirements for secondary roof drainage in the 1990s, the building codes have included such requirements since 1949. The 1949 Uniform Building Code required overflows to be installed at each roof drain at the low point.

The UPC allows the primary storm drainage and the secondary storm drainage to be combined into a common vertical downspout or leader. The IPC and NSPC require the secondary storm drainage to be piped separately to a point of disposal that is visible above or at grade. Both the IPC and UPC require the secondary storm drainage system to be sized for a rainfall occurrence of 60-minute duration and a 100-year return period. The NSPC requires the secondary storm drainage system to be sized for a rainfall occurrence of 15-minute duration and a 100-year return period. The result in the NSPC is a secondary storm drainage system that will flow a greater capacity than the primary storm drainage system.

The IBC clearly states that the roof loading must consider the primary roof drainage means blocked and the rise of water above the secondary roof drain to meet the discharge rates. This is the only code requirement that identifies loading based on the discharge rate and rise of water above the drain. However, the plumbing codes do not provide any discharge rates through secondary roof drains. The interpretation of the IBC is that calculations must be performed to determine the rise of water above the base of the drain. The IBC also requires the roof loading to be evaluated for ponding instability.

older Plumbing Codes

The sizing tables in the UPC and IPC can be traced to ASA A40.8-1955, National Plumbing Code. This code specified storm drainage sizing requirements that are the same as those in the current plumbing codes. The tables in ASA A40.8 were slightly different, listing the values for 4 inches of rainfall. Users of the code were directed to divide the values in the table by four and multiply by the local rainfall rate.

other Reference DocumentsASPE Plumbing Engineering Design Handbook, Volume 2: Plumbing Systems addresses storm drainage design. Chapter 4 identifies the engineering design and specification requirements for a storm drainage system. For sizing the systems, Chapter 4 references the sizing requirements in the plumbing codes. While the philosophical requirements for sizing identify the proper method of sizing, the reference to the plumbing code defers to the sizing requirements that date back to 1955.

RCIP Publication No. 02.03, Roof Drainage, published by the Roof Consultants Institute Foundation, was also reviewed. The sizing of the storm drainage system in this document references the plumbing codes. However, RCIP Publication No. 02.03 includes a method for sizing scuppers for either primary or secondary roof drainage. The sizing method includes a calculation of the height of the water at the scupper while flowing at the required rainfall rate.


Many other documents regard the testing, design, and installation of siphonic roof drainage systems. However, as previously stated, this project specifically excluded siphonic roof drainage since such research has been completed with sizing methods that address all aspects of the storm drainage system.

Referenced standardThe standard for roof drains is ASME A112.6.4. This is the consensus standard referenced in the plumbing codes. ASME A112.6.4 specifies material requirements and dimensional sizing requirements. It does not include test requirements for establishing the flow rate through the roof drain. Furthermore, it does not include drainage opening requirements.

CSA B79 is the Canadian consensus standard for drains, including roof drains. It is similar to the ASME standard in specifying material and dimension requirements.

RooF DRain testingThe testing of the roof drains was divided into two phases. The first phase of testing was a preliminary set of tests performed at SGS U.S. Testing Company in Tulsa. The second phase was a follow-up, detailed set of tests performed at IAPMO R&T Laboratories in Ontario, California.

Preliminary testsThe preliminary tests conducted at SGS U.S. Testing Company were designed to evaluate whether a problem existed with the sizing of storm drainage systems. The cooperating manufacturers supplied a series of roof drains to be tested. Findings from the preliminary testing were published and presented at the 2010 ASPE Convention in Philadelphia.

The previously published results of the preliminary tests are not listed in this report. The preliminary testing indicated the need to do further testing on the roof drains. The additional testing would require more detailed results. To obtain these results, it was determined that different instrumentation and a different test protocol would be necessary.

testing at iaPMo R&t laboratoriesA test protocol was developed for testing that was to be conducted at IAPMO R&T Laboratories. The test protocol was developed by ASPE RF with input from IAPMO R&T Laboratories. The final test protocol approved by the ASPE RF Board of Directors appears in Appendix A.

The test assembly identified in the protocol was constructed at IAPMO R&T Laboratories. Photographs of the test assembly are shown in Appendix B. The photographs show that the test assembly inlet piping was slightly modified from the protocol to reduce wave action in the test box. This was approved prior to the start of testing.

The roof drains were tested with three distinct piping arrangements (see Figure 1). In the first test series, the roof drain was installed without any piping connected to the drain. The intent of this test was to establish a control for the remainder of the testing.

In the second piping arrangement, the roof drain was connected to a straight section of pipe that discharged to the recirculation tank. In the third piping arrangement, the pipe was offset 90 degrees below the roof drain. The horizontal offset length ranged from 4 to 5 feet before turning downward, discharging to the recirculation tank. The third piping arrangement was intended to simulate the most common method of installing the piping connected to the roof drain.


Flow through the drain was measured by the pump flow rate once the roof ponding around the drain achieved steady state. In addition to the flow rate, the velocity of flow in the pipe was measured, as well as the pressure.

Prior to the testing of the roof drains, control tests were run without the roof drain in place. These tests were done for each size opening with a straight pipe and an offset piping arrangement.

A total of 60 roof drains were tested. The test results do not identify the manufacturer’s name or model number of the drain. Each manufacturer was identified randomly with a letter designation. Each drain model was identified consecutively with the prefix being the manufacturer’s letter designation.

The random order of the roof drains is identified in Table 1. These manufacturer and model identifiers are used throughout the report. Table 1 also lists a description of the roof drain and the type of strainer. While the cooperating manufacturers were previously identified in alphabetical order, the list of manufacturers in Table 1 is not in alphabetical order.

FiguRe 1

Modified PipingArrangment

Straight PipingArrangment

No Piping


taBle 1 RooF DRains testeD By iaPMo R&t laBoRatoRies

test no. Company no. Model

no. Description of Roof Drain type of strainer

1 Manufacturer A 1 A-1 2” cast iron drain cast iron dome





6 Manufacturer B 1 B-1 2” cast iron drain cast iron dome




10 Manufacturer C 1 C-1 2” cast iron drain poly dome





15 Manufacturer D 1 D-1 2” cast iron drain aluminum dome




19 Manufacturer E 1 E-1 2” PVC drain poly dome

20 Manufacturer E 2 E-2 4” PVC drain poly dome

21 Manufacturer E 3 E-3 4” PVC drain aluminum dome

22 Manufacturer E 4 E-4 6” PVC drain aluminum dome

23 Manufacturer E 5 E-5 4” cast iron drain poly dome

24 Manufacturer E 6 E-6 6” cast iron drain poly dome

25 Manufacturer E 7 E-7 4” cast iron drain cast iron dome

26 Manufacturer E 8 E-8 6” cast iron drain cast iron dome

27 Manufacturer F 1 F-1 3” cast iron drain cast iron dome








35 Manufacturer G 1 G-1 2” PVC drain ABS dome




39 Manufacturer H 1 H-1 2” cast iron drain cast iron dome




taBle 1 RooF DRains testeD By iaPMo R&t laBoRatoRies

test no. Company no. Model

no. Description of Roof Drain type of strainer



44 Manufacturer I 1 I-1 2” PVC drain poly dome



47 Manufacturer J 1 J-1 2” cast iron drain cast iron dome





52 Manufacturer J 6 J-6 2” cast iron drain brass dome









test ResultsThe test results for each drain are found in Appendix C. The results listed are the raw data reported by IAPMO R&T Laboratories. This is the information that was provided directly from the laboratory.

A table is provided for each drain listing the flow rate, velocity of flow, and pressure in the piping for each of the three piping arrangements. The values published in the table are an average of three tests performed for each value (run) of testing.

The test protocol required the testing to be conducted at ponding levels ranging from 1 inch to 6 inches in height, measured at the roof drain. The ponding levels were increased in increments of 1 inch. When there was no measurable flow at 1 inch of ponding, IAPMO R&T Laboratories tested the drain up to 7 inches of ponding. This was done with only a few drains that had little to no flow at 1 inch of ponding.

The first five test results listed in Appendix C are the control tests that do not have a roof drain connected. These five tests were performed only with straight pipe and the offset piping arrangement.


inteRPRetation oF DataThe raw data was analyzed by comparing the results for roof drains of the same size. For certain sizes, the cooperating manufacturer supplied multiple drains. The data for drains of the same size from the same manufacturer were also compared.

The tables and charts prepared for interpreting the data are identified by number. The numbering scheme used for the tables and charts lists the drain size first. The second number is the test piping arrangement. The number 1 indicates no pipe connected to the drain. The number 2 indicates a straight pipe connected to the drain. The number 3 indicates an offset piping arrangement. For example, Table 4-3 is the table of results for 4-inch drains with an offset piping arrangement. Letters are used to distinguish the different charts. The letter “a” always indicates the chart with all of the drains for the given size and piping arrangement. Letters b, c, d, … are used to identify the charts comparing drains of the same size from the same manufacturer.

For the 4-inch roof drains, there are also charts identified as 4-4 with a letter. These charts are a comparison of each drain for the three different piping arrangements. This was done only for 4-inch drains to show the differences in flow for the same drain, depending on the pipe, or lack thereof, connecting to the drain.

A total of 76 tables and charts compare the data from the tests.

Predictions Prior to testingWith all laboratory testing, engineers attempt to predict the general results of the testing prior to conducting the test. The ASPE RF Board of Directors, in preparing the testing protocol, was no different. The Board attempted to predict, in general terms, the results they anticipated.

Some of the assumptions made regarding the test results were as follows:

• Theflowthroughthedrainwithnopipeconnectedshouldhavethehighestvalue. • Thepipingarrangementmaynotimpacttheflowthroughtheroofdrain. • Thedrainmaygosiphonicduringthetesting. • Theflowrateshouldbesimilarformanufacturers’drainsthatlookidentical. • Thehighflowratesshouldpressurizethepipe.

As previously stated, the purpose of testing the roof drain without any piping was to establish a control value to compare the rest of the data. However, the anticipation that the roof drain without any piping would have the highest flow rates turned out to be wrong. In reviewing the data in Appendix C, for most roof drains the flow rate without any piping connected was the lowest flow rate of the three piping arrangements. The reason for this is further discussed in the Engineering Analysis section.

The assumption that the piping arrangement would have little to no impact on the flow rate also proved to be inaccurate by testing. The drains that looked the same from different manufacturers did not have the same flow rates. This was another assumption that proved to be incorrect.

If the roof drain was subjected to a high enough head height, the flow did go siphonic, even though the roof drains were not a siphonic design. However, for most drains tested, a water head height of 6 inches did not result in the flow going siphonic.

The assumption that the system would pressurize the pipe as the flow increased also proved to be incorrect. The higher flow rates lowered the pressure in the piping. This is further discussed in the Engineering Analysis section.

analysis of testing without Roof DrainThe purpose of testing the piping system without a roof drain was to provide a control value to compare the roof drains. If the flow rates through the roof drains were higher than the opening in the roof test assembly, this would indicate that the dome of the roof drain assisted in increasing the flow rate. If the flow rates were lower, it would indicate that the dome configuration hindered flow through the roof drain. Table 2-0 lists the flow rates without a roof drain in place.


taBle 2-0, CoMPaRison Flow Rates without a RooF DRain

Pipe size

(inch)

Maximum Flow Rate through opening without Roof Drain Based on Ponding height (gpm)

1” 2” 3” 4” 5” 6”

Straight Offset Straight Offset Straight Offset Straight Offset Straight Offset Straight Offset

2 32 23 34 35 35 36 75 64 91 66 178 69

3 50 37 61 64 75 79 101 100 124 129 146 161

4 59 57 121 108 178 141 184 170 208 205 251 247

5 113 124 137 141 199 178 257 207 249 222 318 910

6 107 95 225 210 326 258 743 685 958 911 989 968

The tests without the roof drain also showed the point where the piping arrangement went from an open channel flow to a siphonic flow. This is identified with the lowering of the pressure measured in the piping and a significant increase in flow rate through the opening.

analysis of no Pipe Connected Roof Drain testThe test results shown in Tables 2-1, 3-1, 4-1, 5-1, and 6-1 as well as the associated charts of the data are of little to no value. While it was anticipated that these flow rates would be the highest and useful as control values, the flow rates were most often the lowest flow rates through the roof drain. These values cannot be used as control numbers.

The other reason these values are of little to no use is because plumbing engineers do not install roof drains without any piping connected. The standard practice in the profession is to install the roof drain and provide a piping connection to the drain on the underside of the roof.

The results of the testing with no pipe connected are reported since the testing was part of the research.

analysis of straight Pipe Compared to Pipe with an offsetOne can compare the difference between a roof drain connected to a straight pipe and a roof drain connected to an offset piping arrangement by comparing the X-2 tables to the X-3 tables. For all of the 4-inch drains, charts were prepared showing the difference between the flows for the same roof drain.

For most drains, the flow rate through a straight pipe was very similar to the flow rate through a roof drain with an offset piping arrangement for ponding heights of 3 inches or less. The exception to this is Chart 4-4a on Model A-3. At 3 inches of ponding at the roof drain, the flow in the straight pipe was more than double the flow rate through the offset piping arrangement.

For ponding heights of 4 inches and greater, the flow rate through a straight pipe exceeded the flow rate through an offset piping arrangement. Again, there were some exceptions to this. Chart 4-4e, Chart 4-4h, and Chart 4-4n show a flow slightly greater in the offset piping arrangement than in the straight pipe. This was also the case at 5 inches of ponding for Model E-5 in Chart 4-4g.

There was no consistency in the difference between flow in a straight pipe versus flow in an offset piping arrangement for ponding 3 inches and greater. For instance, in Chart 4-4a, Model A-3, the flow in the straight pipe is more than double the flow in an offset piping arrangement. By comparison, Chart 4-4n, Model J-3 indicates flow rates that are very similar between the two piping arrangements.

analysis oF 2-inCh RooF DRains with stRaight PiPeThe test results show a significant difference in flow rates through different manufacturers’ roof drains. With a ponding of 1 inch, two drains did not have any measurable flow rate. Excluding these two drains, the flow rates at 1 inch of ponding varied from 10 gpm (Model G-1) to a high of 61 gpm (Model B-1). The lowest flow rate, Model G-1, is a PVC drain with a poly dome. The highest flow rate, Model B-1, is a cast iron roof drain with a cast iron dome.

While the materials may initially appear to make a difference in flow rate, the second lowest flow rate was Model H-1 with a flow rate of 11 gpm. Model H-1 is a cast iron roof drain with a cast iron dome.


Comparing these two drains at 6 inches of ponding, Model G-1 had a flow rate of 177 gpm and Model B-1 had a flow rate of 202 gpm, a difference of only 14 percent. The difference between the two flow rates at 1 inch of ponding was 600 percent.

Manufacturer J submitted three 2-inch roof drains for testing. The flow rates between the different models were very similar. The greatest difference was between two of the drains at 5 inches of ponding. One drain flowed 32 percent more than the other. Interestingly, these two drains at 4 inches of ponding had basically the same flow rate.

taBle 2-1

2” RooF DRain test Results

RooF DRain without DRain PiPe

test no. Model no. Description type of strainer

Flow Rate (gpm) Based on head height

1” 2” 3” 4” 5” 6” 7”

1 A-1 2” cast iron drain cast iron dome 41 70 64 73 77 82

6 B-1 2” cast iron drain cast iron dome 53 62 64 69 71 72

10 C-1 2” cast iron drain poly dome 13 49 65 73 80 87

15 D-1 2” cast iron drain Aluminum dome 29 48 51 54 75 83

19 E-1 2” PVC drain poly dome * 45 58 78 95 99 103

35 G-1 2” PVC drain ABS dome 18 40 51 70 78 89

39 H-1 2” cast iron drain cast iron dome 13 52 54 65 74 88

44 I-1 2” PVC drain poly dome ** 38 65 75 67 66

47 J-1 2” cast iron drain cast iron dome 22 54 59 75 81 87

52 J-6 2” cast iron drain brass dome 20 49 55 65 73 82


* No flow

** Flow too low for sensors to record


ChaRt 2-1a

2” RooF DRain CoMPaRison oF test Results


2” Roof Drain Comparison of Test Results

Roof Drain without Drain Pipe

ChaRt 2-1b


RooF DRains oF saMe ManuFaCtuReR



taBle 2-2


RooF DRain with stRaight DRain PiPe

test no.

Model no.

Description type of strainer Flow Rate (gpm) Based on head height

1” 2” 3” 4” 5” 6” 7”




15 D-1 2” cast iron drain aluminum dome 26 76 87 109 122 165




44 I-1 2” PVC drain poly dome * 36 102 126 161 183 177




* Flow too low for sensors to record

ChaRt 2-2a




ChaRt 2-2b





analysis oF 2-inCh RooF DRains with oFFset PiPingThe highest flow rate and lowest flow rate for 2-inch roof drains connected to an offset piping arrangement were the same two drains at 1 inch of ponding, Models G-1 and B-1. The flow rate through Model B-1 was almost six times greater than Model G-1 with 1 inch of ponding. At 6 inches of ponding, Models G-1 and B-1 had similar flow rates. Once the ponding reached 2 inches, the flow rates were closer with these two drains.

Chart 2-3a shows the wide variation in flow rates for the roof drains. Some roof drains discharged almost twice as much as other roof drains with the same ponding of water.

Chart 2-3b shows that the three roof drains from the same manufacturer had similar flow rates. Each drain had flows in the upper end for 2-inch roof drains.

taBle 2-3


RooF DRain with oFFset DRain PiPe

test no.

Model no.


1” 2” 3” 4” 5” 6” 7”








44 I-1 2” PVC drain poly dome * 46 68 83 78 92 96




* Flow too low for sensors to record


ChaRt 2-3a



ChaRt 2-3b





analysis oF 3-inCh RooF DRains with stRaight PiPeWith the larger 3-inch roof drains, there is a great difference in the flow rates between the different manufacturers’ roof drains. With 1 inch of ponding, the lowest flow rate was 13 gpm through Model I-2. This is a PVC drain with a poly dome.

The greatest flow rate at 1 inch of ponding was Model F-1, flowing 105 gpm. Model F-1 is a cast iron drain with a cast iron dome. The Model F-1 flow rate is more than eight times more than the flow rate of Model I-2. With 4 and 5 inches of ponding, the Model I-2 flow rate exceeded the Model F-1 flow rate.

At 6 inches of ponding, the lowest flow rate was 429 gpm for two models. The highest flow rate was 522 gpm for three different models. The greater difference was at 5 inches of ponding. The lowest flow rate was 186 gpm, while thehighestflowratewas490gpm,morethan2-1/2timesthelowestflowrate.

Two charts show the same manufacturer’s drains of the same size. The two models from Manufacturer F did not have similar flow rates. Model F-1’s flows at 1 inch, 2 inches, and 6 inches of ponding exceed the flow rates of Model F-5, while Model F-5 had greater flows at 3 inches through 5 inches of ponding.

Manufacturer J has three 3-inch roof drains. Models J-2, J-7, and J-13 were similar at 1 and 2 inches of ponding. The flow rates between the drains varied significantly for the other ponding levels of 3 through 5 inches. At 6 inches of ponding, the flow rates were similar.

taBle 3-1



test no.

Model no.


1” 2” 3” 4” 5” 6”





27 F-1 3” cast iron drain cast iron dome 120 168 225 212 244 313




45 I-2 3” PVC drain poly dome 12 93 147 233 292 340





ChaRt 3-1a



ChaRt 3-1b





ChaRt 3-1c




taBle 3-2



test no.

Model no.


1” 2” 3” 4” 5” 6”














ChaRt 3-2a



ChaRt 3-2b





ChaRt 3-2c





analysis oF 3-inCh RooF DRains with oFFset PiPingThe great difference in the flow rates between the different manufacturers’ roof drains continues with 3-inch roof drains connected to an offset piping arrangement. With 1 inch of ponding, the lowest flow rate was 14 gpm through Model I-2. This is a higher value, by 1 gpm, than the drain flow through straight pipe.

The greatest flow rate at 1 inch of ponding was Model F-1, flowing 118 gpm. That is more than eight times the flow rate of Model I-2. Models F-1 and I-2 did not have similar flows until the ponding reached 5 inches.

Even with 6 inches of ponding, there was a significant difference between the highest flow rate and the lowest flow rate. Model J-2 had a flow of only 195 gpm, while Model F-1 had a flow rate of 423 gpm. That amounts to more than 217 percent greater flow through Model F-1 compared to Model J-2.

Two charts show the same manufacturer’s drains of the same size. The two drains from Manufacturer F had similar flow rates. Although there were slight differences, the differences were not consistent. Model F-1 flows were higher at 1 inch, 2 inches, and 6 inches of ponding, while Model F-5 had greater flows at 3 inches through 5 inches of ponding.

Chart 3-3c compares the three roof drains from Manufacturer J. Models J-2 and J-13 were similar through 5 inches of ponding. At 6 inches of ponding, Model J-13 had a significantly higher flow rate than Model J-2, 195 gpm versus 358 gpm.

taBle 3-3



test no.

Model no.


1” 2” 3” 4” 5” 6”














ChaRt 3-3a



ChaRt 3-3b





ChaRt 3-3c





analysis oF 4-inCh RooF DRains with stRaight PiPeThe difference in flow rates continued for 4-inch roof drains. With 1 inch of ponding, the lowest flow rate was 16 gpm for two drains, Models E-5 and I-3. Model E-5 is a cast iron drain with a poly dome, and Model I-3 is a PVC drain with a poly dome.

The highest flow rate at 1 inch of ponding was Model F-2 with 117 gpm. Model F-2 is a cast iron drain with a cast iron dome.

Model E-5 has lower flow rates than most of the drains through 5 inches of ponding. At 6 inches of ponding, the flow rate more than triples from 5 inches of ponding.

Model I-3 had similar lower flow rates through 4 inches of ponding. At 5 inches of ponding, the flow rate more than doubled the flow rate at 4 inches. Similarly, at 6 inches of ponding, the flow rate more than doubled again from 5 inches of ponding.

At 6 inches of ponding, the greatest flow rate was 889 gpm though Model C-3. The lowest flow rate was 628 gpm though Model J-3.

Three manufacturers submitted multiple 4-inch roof drains. One roof drain from Manufacturer E had a flow rate of 657 gpm with 5 inches of ponding, while another one of its drains had a flow rate of only 215 gpm. This is the greatest difference in flow rates for a single manufacturer with the same size drains.

taBle 4-1



test no.

Model no.


1” 2” 3” 4” 5” 6”





20 E-2 4” PVC drain poly dome 58 113 166 210 270 302

21 E-3 4” PVC drain aluminum dome 26 90 189 230 242 257

23 E-5 4” cast iron drain poly dome 17 76 162 180 215 296

25 E-7 4” cast iron drain cast iron dome 72 180 253 225 295 360





46 I -3 4” PVC drain poly dome 12 93 147 233 292 340





ChaRt 4-1a



ChaRt 4-1b





ChaRt 4-1c




ChaRt 4-1d





taBle 4-2



test no.

Model no.


1” 2” 3” 4” 5” 6”


















ChaRt 4-2a



ChaRt 4-2b





ChaRt 4-2c




ChaRt 4-2d





analysis oF 4-inCh RooF DRains with oFFset PiPingModel F-2 remained the highest and Model I-3 remained the lowest flow rate when connected to an offset piping arrangement with 1 inch of ponding. The lowest flow rate was 14 gpm, and the highest was 118 gpm.

The flow rate trend lines were similar to the straight pipe connection for the 4-inch roof drains connected to an offset piping arrangement. However, the flow rates were lower.

The lowest flow rate with 6 inches of ponding was 423 gpm for Model E-5. The highest flow rate was 710 gpm for Model B-3.

taBle 4-3



test no.

Model no.


1” 2” 3” 4” 5” 6”


















ChaRt 4-3a



ChaRt 4-3b





ChaRt 4-3c




ChaRt 4-3d





analysis oF PeRFoRManCe oF inDiviDual 4-inCh RooF DRainsAs previously stated, a chart (identified as 4-4 with a letter) compares the flow rates of the three piping arrangements for each 4-inch roof drain. Since the flow rates for the roof drain with no piping connected provided no useful information, the trend line for this flow rate can be ignored on these charts. The two trend lines that need to be compared are the trend line for a roof drain connected to a straight pipe and a roof drain connected to an offset piping arrangement.

With lower ponding heights, the difference in flow rate between a straight pipe and an offset piping arrangement is not significant. As the ponding increases, the flow in the straight pipe is greater than the offset piping arrangement. This tends to occur at 4 inches or greater of ponding. However, there are exceptions with certain roof drains.

ChaRt 4-4a

4” RooF DRain MoDel a-3

CoMPaRison oF test Results


ChaRt 4-4b

4” RooF DRain MoDel B-3


ChaRt 4-4c

4” RooF DRain MoDel C-3



ChaRt 4-4d

4” RooF DRain MoDel D-3


ChaRt 4-4e

4” RooF DRain MoDel e-2



ChaRt 4-4f



ChaRt 4-4g




ChaRt 4-4h



ChaRt 4-4i

4” RooF DRain MoDel F-2



ChaRt 4-4j

4” RooF DRain MoDel F-6


ChaRt 4-4k

4” RooF DRain MoDel g-3



ChaRt 4-4l

4” RooF DRain MoDel h-3


ChaRt 4-4m

4” RooF DRain MoDel i-3



ChaRt 4-4n

4” RooF DRain MoDel J-3


ChaRt 4-4o




ChaRt 4-4p




analysis oF 5-inCh RooF DRains with stRaight PiPeThe fewest number of roof drains for testing were 5 inches in size—only eight roof drains from five manufacturers.

The 5-inch roof drains with the lowest and highest flow rates at 1 inch of ponding were from the same manufacturer, Manufacturer J. Model J-10 had the lowest flow rate at 97 gpm, while Model J-4 had the highest flow rate at 162 gpm. Model J-4 is a cast iron drain with a cast iron dome. Model J-10 is a cast iron drain with a brass dome.

With 6 inches of ponding, the highest flow rate was 1,267 gpm through Model C-4. The lowest flow rate was Model J-4 at 651 gpm. At 1 inch of ponding, Model J-4 had the highest flow rate. At 6 inches of ponding, it had the lowest flow rate.

The comparison between the Manufacturer J models is shown in Chart 5-3b. The trend lines in this chart appear similar to the trend lines for Manufacturer J’s 4-inch roof drains.

taBle 5-1



test no.

Model no.


1” 2” 3” 4” 5” 6”










ChaRt 5-1a



ChaRt 5-1b





taBle 5-2



test no.

Model no.


1” 2” 3” 4” 5” 6”

4 A-4 5” cast iron drain cast iron dome 109 220 617 1,203 1,125 1,042

13 C-4 5” cast iron drain poly dome 118 199 402 745 1,060 1,267



42 H-4 5” cast iron drain cast iron dome 128 184 264 484 716 1,016


55 J-10 5” cast iron drain brass dome 97 152 236 371 646 1,012


ChaRt 5-2a




ChaRt 5-2b





analysis oF 5-inCh RooF DRains with oFFset PiPingThe lowest flow rate with 1 inch of ponding and an offset piping arrangement was Model F-3 with a flow rate of 25 gpm. This is significantly less than the flow in the same drain with straight pipe. That flow rate was 134 gpm. Model F-3 is a cast iron drain with a cast iron dome.

The highest flow rate at 1 inch of ponding was Model F-7 with 148 gpm. This is another case where the same manufacturer has the highest and lowest flow rate for two different models.

With 6 inches of ponding, J-4 remains the lowest flow rate with 618 gpm. The highest flow rate was still Model C-4 with 973 gpm.

The comparison of Manufacturer J’s roof drains shows similar trend lines to the straight piping flow rates.

taBle 5-3



test no.

Model no.


1” 2” 3” 4” 5” 6”










ChaRt 5-3a



ChaRt 5-3b





analysis oF 6-inCh RooF DRains with stRaight PiPeThe roof drain with the lowest flow rate with 1 inch of ponding was Model E-4, with a flow rate of 20 gpm. Model E-4 is a PVC drain with an aluminum dome.

The highest flow rate with 1 inch of ponding was Model F-8 with 153 gpm. Model F-8 is a cast iron drain with a cast iron dome. The difference is more than seven times between the highest and the lowest.

With 6 inches of ponding, the highest flow rate was Model B-4 with a flow rate of 1,520 gpm. Model B-4 is a cast iron drain with a cast iron dome. The lowest flow rate is Model J-5 with a flow rate of 668 gpm, less than half the highest flow rate. Model J-5 is a cast iron drain with a cast iron dome.

taBle 6-1



test no.

Model no.


1” 2” 3” 4” 5” 6”















ChaRt 6-1a



ChaRt 6-1b





ChaRt 6-1c




ChaRt 6-1d





taBle 6-2



test no.

Model no.


1” 2” 3” 4” 5” 6”

5 A-5 6” cast iron drain cast iron dome 122 169 744 979 1,162 1,188

9 B-4 6” cast iron drain cast iron dome 111 188 382 629 1,034 1,520





26 E-8 6” cast iron drain cast iron dome 91 262 392 564 864 1,471


34 F-8 6” cast iron drain cast iron dome 153 156 347 534 803 1,062

38 G-4 6” PVC drain ABS dome 118 112 240 462 764 1,142



56 J-11 6” cast iron drain brass dome 94 117 227 393 613 1,147

ChaRt 6-2a




ChaRt 6-2b




ChaRt 6-2c





ChaRt 6-2d





analysis oF 6-inCh RooF DRains with oFFset PiPingThe roof drain with the lowest flow rate with 1 inch of ponding was Model H-5, with a flow rate of 10 gpm. Model H-5 is a cast iron drain with a cast iron dome. This compares to a flow rate of 28 gpm with a straight pipe connecting.

The highest flow rate with 1 inch of ponding was Model A-5 with 228 gpm. Model A-5 is a cast iron drain with a cast iron dome. This flow rate is 22 times greater than the lowest flow rate. The flow rate is higher than the flow rate for straight pipe for this roof drain.

With 6 inches of ponding, the highest flow rate was Model C-5 with a flow rate of 1,380 gpm. Model C-5 is a cast iron drain with a poly dome. The lowest flow rate is still Model J-5 with a flow rate of 639 gpm, again less than half the highest flow rate.

taBle 6-3



test no.

Model no.


1” 2” 3” 4” 5” 6”

5 A-5 6” cast iron drain cast iron dome 228 240 549 1,008 1,014 1,026

9 B-4 6” cast iron drain cast iron dome 115 194 367 598 1,011 1,265





26 E-8 6” cast iron drain cast iron dome 186 233 409 511 754 1,258

30 F-4 6” cast iron drain cast iron dome 117 210 401 596 916 1,164


38 G-4 6” PVC drain ABS dome 101 108 248 450 718 1,120





ChaRt 6-3a



ChaRt 6-3b





ChaRt 6-3c




ChaRt 6-3d





engineeRing analysisThe test results show a wide variety of flows through roof drains. The flow rates exhibited no consistency or pattern.

Before the study started, ASPE RF asked the manufacturers what the flow rates were through their roof drains. None of the manufacturers knew. The response was the same: “The roof drains are designed to meet the standard.” All of the roof drains were listed to ASME A112.6.4, thus meeting the requirements of the standard. However, the standard does not specify any flow requirements.

The sizing method in the plumbing codes relies on a consistent flow through the roof drains. The plumbing codes assume that as the water reaches the roof drain, the water simply proceeds down the storm drain pipe. However, that is not the case.

Another fallacy in the sizing method listed in the plumbing codes is that the roof drains will only discharge the amount of water to meet the maximum capacity of the storm drainage pipe. Without some means of restricting the flow into a roof drain, the drain will flow the amount of water based on the head height of ponding around the drain. However, the head height of ponding will vary depending on the slope of the roof, the location of the roof drain, and the amount of rainfall.

Structuralengineersandarchitectsspecifyaminimumslopeof1/4inchperfootonflatroofs.Manyroofsarepitched greater than this amount. The greater the pitch of the roof, the faster the water arrives at the roof drain. The faster the water arrives, the greater the depth of ponding at the roof drain. Finally, the greater the depth of ponding, the greater the flow rate through the roof drain.

If the flow exceeds the maximum capacity of the storm drainage pipe, open channel flow cannot be guaranteed. When the flow is no longer open channel flow, the pressure excursions in the piping system can be significant. The storm drainage piping system is designed and installed for open channel flow. Hence, if open channel flow is exceeded, the piping system can be damaged from a high pressure differential. This would be the most likely reason for hangers being ripped from reinforced concrete floors, pipe bursting apart, water running out on balcony decks, and components in the piping system being destroyed.

Table 7 shows the maximum flow rate measured through roof drains at a given level of ponding. Column 2 lists the maximum allowable flows through a vertical storm drain of the same diameter. The numbers in column 2 are taken from the Plumbing Engineering and Design Handbook of Tables.

As can be seen in the table, 83 percent of the maximum flow rates exceeds the flow rate in the piping of the same size. A heavy black line in the table distinguishes the allowable flows in the drain from the flows that are too high. For 2-inch and 3-inch roof drains, every maximum flow rate from 1 inch of ponding through 6 inches of ponding exceeds the allowable flow in a vertical pipe of the same size.

taBle 7, CoMPaRison oF RooF DRain Flow Rates to veRtiCal DRain CaPaCity

Pipe size

(inches)

vertical Drain (gpm)

Maximum Flow Rate through Roof Drain Based on Ponding height (gpm)

1” 2” 3” 4” 5” 6”


2 34 61 59 171 134 177 149 192 151 206 157 208 161

3 87 105 118 220 185 415 351 468 347 490 384 522 410

4 180 117 118 217 210 538 445 754 615 865 668 889 710

5 311 162 148 222 258 617 641 1203 867 1,125 947 1,267 973

6 538 153 228 262 240 744 549 979 1,008 1,167 1,157 1,630 1,380

It is recognized that there are lower flow rates for the various drains tested. Table 7 merely shows that the maximum flow rates for most of the drains allow too much flow into a vertical pipe of the same diameter.

Using the maximum allowable flow rate in column 2 of Table 7, a 2-inch roof drain with 1 inch of ponding would have to connect to a 3-inch vertical storm drain. Similarly, a 3-inch roof drain with 1 inch of ponding would have to connect to a 4-inch vertical storm drain.


If you increase the ponding to 2 inches, a 2-inch roof drain would have to connect to a 4-inch storm drain. A 3-inch roof drain would have to connect to a 5-inch drain.

The values in Table 7 can be compared to the controlled measurements of the test assembly without any roof drain connected. Table 8 provides a comparison of the opening without a roof drain to the maximum flow rate measured through the roof drains that were tested.

taBle 8, CoMPaRison oF oPening Flow Rates to MaXiMuM RooF DRain Flow Rates

Pipe size

(inches)

vertical Drain (gpm)

Maximum Flow Rate through Roof Drain Based on Ponding height (gpm)

1” 2” 3” 4” 5” 6”


2 Open 32 23 34 35 35 36 75 64 91 66 178 69

2 Drain 61 59 171 134 177 149 192 151 206 157 208 161

3 Open 50 37 61 64 75 79 101 100 124 129 146 161

3 Drain 105 118 220 185 415 351 468 347 490 384 522 410

4 Open 59 57 121 108 178 141 184 170 208 205 251 247

4 Drain 117 118 217 210 538 445 754 615 865 668 889 710

5 Open 113 124 137 141 199 178 257 207 249 222 318 910

5 Drain 162 148 222 258 617 641 1,203 867 1,125 947 1,267 973

6 Open 107 95 225 210 326 258 743 685 958 911 989 968

6 Drain 153 228 262 240 744 549 979 1,008 1,167 1,157 1,630 1,380

Comparing every value, the flow rate through the roof drain exceeds the flow rate through an opening without a roof drain. For maximum flow rate conditions, this indicates that the dome and shape of the roof drain assist in the removal of water off the roof. While the table appears to validate all roof drains, the statement made regarding the performance of the roof drain cannot be made for every roof drain tested. Some roof drains had values that were lower than an opening without a roof drain.

It was decided not to include the trend line for the test of the opening without a roof drain. If the trend line was added to charts 2-1a through 6-3d, it would get lost somewhere along the bottom of the chart. To demonstrate the location of the no roof drain flow rate to the roof drains, Chart 8-2 duplicates the 5-inch roof drain with straight pipe chart with the open pipe added.


ChaRt 8-2, 5” RooF DRain stRaight PiPe with oPen PiPe inCluDeD

The trend line for the open drain is the lowest line at 6 inches of ponding. Following the line across the chart, a few drains discharge a lower flow rate than the opening in the roof assembly with 1 inch or less of ponding.

One of the benefits of the testing without a roof drain is that these flow rates can be used when sizing the secondary or emergency storm drainage system. Most secondary storm drainage systems are an open pipe without a roof drain or dome strainer.

When using the test results, it should be noted that the flow rates for many flows are siphonic. If the secondary storm drain opens to atmosphere aboveground, the listed flow rates can be used. Both the IPC and NSPC require the secondary storm drainage to terminate atmospherically above grade.

If the secondary storm drainage system connects to the public storm sewer, the flow rates may not be accurate. Testing was not performed to determine if the flow in the piping becomes siphonic when connected to a public storm sewer system. Additional testing would be necessary to determine the flow rates to use for open pipe connected to a public storm sewer.

The result of the testing illustrates that the sizing method in the plumbing codes is incorrect. In some instances, the sizing may be off by two pipe diameters.

Knowing the inadequacy of the storm drainage sizing in the plumbing codes, the question becomes: Why haven’t more storm drainage systems failed on commercial buildings?

There are many answers to this question. The first reason is because the rainfall rate for the design of storm drainage systems is a 60-minute storm with a 100-year return period. These rainfalls do not occur very often. However, it should be noted that some storm drainage systems have failed during a microburst, or a heavy downpour in a very short period, giving credence to adding a second calculation for the ponding of water that occurs during a five-minute storm with a 10-year return period or a 15-minute storm with a 100-year return period. This is the rainfall rate that would occur during a microburst. While not a lot of water in inches falls on the ground, for a steeper slope roof, a lot of water can arrive at the roof drain quickly.

Another reason for not having a significant number of failures is the plumbing engineering community oversizing storm drainage systems. It is not unusual for a storm drainage piping design to result in the pipe being two pipe diameters larger than is required by the plumbing codes. The larger pipe can handle the higher flows through the roof drains when ponding around the drain occurs.


Structural engineers are also known for over-designing the roof to handle great roof loads. This has also prevented a significant number of roof failures.

With the increase in value engineering, storm drainage systems are being redesigned for small pipe sizes. Some of the failures that have occurred were in systems that were value engineered. This should not be considered a condemnation of value engineering. Value engineering always has its place in engineering design. Value engineering merely revealed the problems with the sizing methods in the plumbing codes.

Since the 1990s, secondary roof drains have been installed on a regular basis, and they even have been installed on some buildings dating back to 1949. In many instances, the secondary roof drainage system prevented the primary roof drainage system from exceeding its capacity.

Finally, the piping systems are typically more robust than is necessary for open channel flow storm drainage systems. The piping systems have been able to withstand the pressure excursions that have occurred in the system.

Pressure Measured in the Piping systemDuring the testing of the roof drains, the pressure in the piping system was measured. This is reported in Appendix C. Not much has been written about the pressure measurements in the analysis of the test. The reason for not mentioning the pressure is because of the invalidity of the results.

After the testing was completed and the data analyzed, it was realized that the test setup did not facilitate the measuring of pressure in the piping system. Most of the pressure readings were negative numbers or vacuum pressures.

When there is open channel flow in a vertical pipe, the top of the stack will have negative pressure. The greater the flow, the higher the negative pressure. This was verified many years ago during testing at the National Bureau of Standards.

When you exceed the capacity of flow for open channel flow, the piping system either converts to pressurized flow or siphonic flow. For most storm drainage systems, it is anticipated that the flow switches to pressure flow. This may or may not be the case since this was not tested.

The problem with the test setup was that the piping terminated above the recirculation tank. With a termination to atmosphere, above the water level in the tank, the system induced siphonage. All of the pressure readings for the higher flows in the roof drains indicate pressures associated with siphonic flow.

For valid pressure readings to be made, the pipe would have to connect to an underground storm drain, storm sewer, and public sewer. For testing purposes, this would result in a tremendous waste of test water due to the lack of recirculation.

An alternative to connecting the piping to an underground storm sewer would be termination below the water level at a point that equates to a long run of piping to a public storm sewer. It should be noted that both pressure flows and siphonic flows allow a greater flow rate though the piping than open channel flow.

sizing Method RecommendationBased on the results of the testing, the plumbing engineering profession must establish a new and proper method for sizing storm drainage systems. The new sizing method must be based on the capacity of the roof drain, the maximum amount of ponding under various storm conditions at the roof drain, and the maximum capacity of the piping system.

The archaic method of using roof area needs to be abandoned. The roof area method does not address the pitch and roughness of the roof, resulting in ponding at the roof drain. The method also does not consider the flow rate through the roof drain.

The ASME A112.6.4 standard regulates the design and construction of roof drains. An important part of this standard should include the performance of the roof drain. This would include the flow rate through the roof drain at various ponding heights.


ASME A112.6.4 needs to add a test for flow rate through a roof drain. The testing for flow rate should utilize the test setup developed by ASPE RF. This test setup has proven to be an accurate method of testing the flow rate through roof drains.

Testing of both straight pipe connections and offset piping must be performed. While one might argue that only an offset piping arrangement needs to be used for testing purposes, if a straight piping arrangement is installed in a building, the flow in the storm drainage pipe could exceed the capacity of the piping system. The design would be inaccurate.

Each manufacturer must publish the flow rates through their roof drains based on head height of ponding. While ASPE RF used 1-inch increments, manufacturers can choose to use smaller increments. ASPE RF is of the opinion that a 1-inch increment is the largest increment that should be used. A maximum ponding height of 6 inches for testing is not unreasonable. However, a manufacturer could always test for a greater amount of ponding.

Recommended Change to asMe standardThe following test protocol is recommended to be added to ASME A112.6.4:

7.2 Flow test

7.2.1 Each roof drain model shall be tested for the flow rate through the drain at 1 inch to 6 inches of ponding water.

7.2.2 Test Assembly. A test assembly shall be constructed as shown in Figure 10 and Figure 11. The piping from the test box shall be the same pipe size as the roof drain being tested.

A flow meter or data acquisition system shall measure flow rates to an accuracy of ±5 gpm.

7.2.3 Test Protocol. Connect the roof drain to the opening in the test pan. For each roof drain, complete the testing in accordance with paragraph 7.2.3.1 and 7.2.3.2.

7.2.3.1 Straight Pipe Test. Connect a minimum of a 10-foot length of drain pipe to the pan with the pipe directed vertically downward. The pipe shall extend to below the water line in the recirculation tank. There shall be no fitting at the bottom of the pipe. With water flowing into the pan, the level of the water shall be controlled to be set above the opening at 1-inch intervals. Begin with a water head of 1 inch, and increase at 1-inch increment up to 6 inches. Achieve a steady state to record the flow of water. Steady state is defined as theconditioninwhichtheheadheightismaintainedwithin+/–0.1inchoftheheadheightforaperiodoffiveminutes. At each head increment, record the flow rate through the roof drain.

7.2.3.2 Offset Piping Arrangement Test. Connect the roof drain to a 1-foot length of pipe that connects to a 90-degreeelbow.Connecta5-footsectionofpipetotheelbow,withthepipepitched1/4inchperfootdownfrom the elbow. Connect a second elbow to the 5-foot section of pipe with the elbow facing downward. Connect a minimum of a 9-foot section of pipe to the elbow and allow it to discharge downward without a fitting on the other end. The pipe shall extend to below the water line in the recirculation tank. With water flowing into the pan, the level of the water shall be controlled to be above the opening at 1-inch intervals. Begin with a water head of 1 inch, and increase at 1-inch increments up to 6 inches. Achieve a steady state to record the flow of water.Steadystateisdefinedastheconditioninwhichtheheadheightismaintainedwithin+/–0.1inchofthehead height for a period of five minutes. At each head increment, record the flow rate through the roof drain.

7.2.4 Test results. Manufacturer shall publish the flow rates for each roof drain based on the piping arrangement (straightpipe/offsetpipingarrangement)andtheheadheightofponding.


FiguRe 10


FiguRe 11


Once the flow rate data is published by the roof drain manufacturers, plumbing engineers will have the data necessary to design the storm drainage system. The remaining information required for the design is the rainfall rate and the capacity of the piping system.

Recommended Change to Plumbing CodesThe plumbing codes must be modified to add new sizing requirements for storm drainage systems. The new sizing method should include sizing based on two rainfall rates. The 60-minute storm with a 100-year return period should remain the design criteria for storm drainage systems. In addition, a five-minute storm with a 10-year return period should be added to the plumbing codes. The sizing of the system should include calculations for the maximum ponding at the roof drain based on these two storms. It is recognized that only one storm will regulate the size. However, without knowing the configuration of the roof, it is impossible to determine which storm will result in the greatest amount of ponding at the roof drain.

The recommended language that should be added to the plumbing codes for sizing a storm drainage system is as follows:

Roof drain flow rate. The flow rate capacity of the roof drain shall be published based on the head height of water at the roof drain. The roof drain flow rate shall be used to size the storm drainage system. The flow rate used for sizing the storm drainage piping shall be based on the maximum anticipated ponding at the roof drain based on a rainfall rate of a 60-minute storm with a 100-year return period and a five-minute storm with a 10-year return period.

Sizing storm drain piping. Vertical and horizontal storm drain pipe shall be sized based on the flow rate through the roof drain. Storm drain pipes shall not exceed the flow rate specified in Table A.

taBle a

stoRM DRain PiPe siZing

Pipe size

(inches)

Maximum Permitted Flow Rate (gpm)

vertical DrainHorizontal Drain Based on Pitch

1/16in/ft 1/8in/ft 1/4in/ft 1/2in/ft

2 34 15 22 31 44

3 87 39 55 79 111

4 180 81 115 163 231

5 311 117 165 234 331

6 538 243 344 487 689

8 1,117 505 714 1,010 1,429

10 2,050 927 1,311 1,855 2,623

12 3,272 1,480 2,093 2,960 4,187

15 5,543 2,508 3,546 5,016 7,093

Note: The values in the table are taken from the Plumbing Engineering and Design Handbook of Tables.


Sizing vertical gutters. Vertical gutters shall be sized based on the flow rate from the horizontal gutters or through the roof drain. Vertical storm drain gutters shall not exceed the flow rate specified in Table B.

taBle B

veRtiCal gutteR siZing

size of leader (inches)

Maximum Permitted Flow Rate (gpm)

2 30

2 x 2 30

11/2 x 21/2 30

21/2 54

21/2 x 21/2 54

3 92

2 x 4 92

21/2 x 3 92

4 192

3 x 41/2 192

31/2 x 4 192

5 360

4 x 5 360

41/2 x 41/2 360

6 563

5 x 6 563

51/2 x 51/2 563

8 1,208

6 x 8 1,208

Note: Single-digit numbers are diameters; other values are square of rectangular shapes. The values in the table are taken from the Plumbing Engineering and Design Handbook of Tables.


Size of horizontal gutters. Horizontal gutters shall be sized based on the flow rate from the roof surface. Horizontal storm drain gutters shall not exceed the flow rate specified in Table C.

taBle C

hoRiZontal gutteR siZing

Diameter of gutter

(inches)

slope

(in/ft)

Capacity

(gpm)

11/2 x 21/2 1/4 26

11/2 x 21/2 1/2 40

4 1/8 39

21/2 x 3 1/4 55

21/2 x 3 1/2 87

5 1/8 74

4 x 21/2 1/4 106

3 x 31/2 1/2 156

6 1/8 110

3 x 5 1/4 157

3 x 5 1/2 225

8 1/16 172

8 1/8 247

41/2 x 6 1/4 348

41/2 x 6 1/2 494

10 1/16 331

10 1/8 472

5 x 8 1/4 651

4 x 10 1/2 1,055

Note: Single-digit numbers are diameters; other values are square of rectangular shapes. The values in the table are taken from the ASPE Plumbing Engineering and Design Handbook of Tables.


aPPenDiX a test PRotoCol DeveloPeD By asPe ReseaRCh FounDation

1.0 Purpose:(a) To engage in scientific research and to produce and disseminate to the general public educational and technical materials devoted to the advancement of plumbing technology and design. (b) To determine the flow rates through roof drains based on the head height of water at the roof drain. (c) To determine the velocity of flow in the vertical drain connected to a roof drain based on the discharge through the roof drain.

2.0 Product to be tested: Roof Drains: The American Society of Plumbing Engineers Research Foundation provided roof drains in sizes 2 inches through 6 inches from various manufacturers.

3.0 Test Assembly: See below figures. The piping from the test box shall be regular PVC of the same pipe size as the roof drain being tested. Standard PVC fittings (white in color) were used for joining the pipe sections. A data acquisition system was used in collaboration with visual observation to record all measurements.

4.0 Test Protocol: Prior to testing the roof drains of a given size, two control tests, as described in sections 4.1 and 4.2, were conducted. A total of 12 control tests (pipe only) were performed. The control test protocol was as follows:

4.1 Connect the pipe to the test box without a roof drain in place. Have the connection sealed to the bottom of the box with a flange to allow full flow into the pipe. Connect a drain pipe of 10 feet in length to the box with the pipe directed vertically downward. There was no fitting at the bottom of the pipe. With water flowing into the box, the level of the water was set above the opening at 1-inch intervals. Begin with a water head of 1 inch, and increase at 1-inch increments up to 6 inches. Achieve a steady state to record the flow of water. At each head increment, record the following information:

4.1.1 Head height of the water

4.1.2 Flow rate of water into the box

4.1.3 Velocity of flow in the stack

4.1.4 Pressure in the stack

The velocity and pressure measurement in the stack shall be taken at three separate locations. Steady stateisdefinedastheconditioninwhichtheheadheightismaintainedwithin+/–0.1inchoftheheadheight for a period of five minutes.

4.2 Repeat the testing with a modified piping arrangement. Connect the drain to the flange with a 1-foot section of pipe that connects to a 90-degree elbow. Connect a 5-foot section of pipe to the elbow, with the pipepitched1/4inchperfootdownfromtheelbow.Connectasecondelbowtothe5-footsectionofpipewith the elbow facing downward. Connect a 9-foot section of pipe to the elbow and allow it to discharge downward without a fitting on the other end. Do not have any fitting at the bottom of the pipe. With water flowing into the box, set the level of the water above the opening at 1-inch intervals. Begin with a water head of 1 inch, and increase at 1-inch increments up to 6 inches. Achieve a steady state to record the flow of water. At each head increment, record the following information:



4.2.3 Discharge flow rate

4.2.4 Velocity of flow in the stack, horizontal pipe, and the second stack


4.2.5 Pressure in the stack, horizontal pipe and the second stack

Steadystateisdefinedastheconditioninwhichtheheadheightismaintainedwithin+/–0.1inchofthehead height for a period of five minutes.

For each drain, the following three tests need to be done: (a) Drain-only test (b) Drain stack configuration (c) Drain alternate configuration

The control protocol shall be as follows:

4.3 Drain Only Test: Connect the roof drain to the opening in the test box. No piping was connected to the test box. With water flowing into the box, set the level of the water above the opening at 1-inch intervals. Begin with a water head of 1 inch, and increase at 1-inch increments up to 6 inches. Achieve a steady state to record the flow of water. At each head increment, record the following information:




4.3.4 Velocity of flow

4.3.5 Pressure


4.4 Drain Stack Configuration: Connect the roof drain to the opening in the test box. Connect 10 feet of pipe to the bottom of the roof drain with the pipe directed vertically downward. Do not have any fitting at the bottom of the pipe. With water flowing into the box, set the level of the water above the opening at 1-inch intervals. Begin with a water head of 1 inch, and increase at 1-inch increments up to 6 inches. Achieve a steady state to record the flow of water. At each head increment, record the following information:





4.4.5 Pressure in the stack, horizontal pipe, and the second stack


4.5 Drain Alternate Configuration: Repeat the testing described in section 4.4 with a modified piping arrangement. Connect the roof drain to a 1-foot section of pipe that connects to a 90-degree elbow. Connecta5-footsectionofpipetotheelbow,withthepipepitched1/4inchperfootdownfromtheelbow.Connect a second elbow to the 5-foot section of pipe with the elbow facing downward. Connect a 9-foot section of pipe to the elbow and allow it to discharge downward without a fitting on the other end. With water flowing into the box, set the level of the water above the opening at 1-inch intervals. Begin with a water head of 1 inch, and increase at 1-inch increments up to 6 inches. Achieve a steady state to record the flow of water. At each head increment, record the following information:






4.5.5 Pressure in the stack, horizontal pipe, and the second stack



aPPenDiX B test asseMBly Photos


aPPenDiX C test Results oF RooF DRains

test 0-2, 2” oPening without a RooF DRain

no DRain with 10-Ft PiPe

Water head (inch) 1” 2” 3” 4” 5” 6”

Flow of water into box (gpm) 32 34 35 75 91 178

Velocityindrainpipe(ft/s) 5.4 5.7 6.3 6.8 7.8 9.0

Pressure in drain pipe (in. W.C.) 0.4 0.0 0.0 0.4 0.5 0.4

DRain with MoDiFieD PiPes

Water head (inch) 1” 2” 3” 4” 5” 6”


Velocityin1ststack(ft/s) 3.4 3.7 4.0 5.4 4.5 6.3

Velocityinhorizontalpipe(ft/s) 2.3 2.7 2.7 5.0 3.5 6.2

Velocityin2ndstack(ft/s) 7.2 7.3 7.9 8.1 8.5 8.1

Pressure in 1st stack (in. W.C.) 0.2 0.3 0.4 -15 -16 -17

Pressure in horizontal pipe (in. W.C.) 2.6 2.4 2.1 -23 -24 -26

Pressure in 2nd stack (in. W.C.) -0.9 -0.9 -1.2 -32 -31 -31



Water head (inch) 1” 2” 3” 4” 5” 6”


Velocity in drain pipe (ft/s) 7.1 7.0 6.2 7.8 8.1 8.2

Pressure in drain pipe (in. W.C.) -0.3 -8.1 -19.4 -39.8 -40.1 -42.2


Water head (inch) 1” 2” 3” 4” 5” 6”


Velocity in 1st stack (ft/s) 3.4 4.7 5.0 8.4 8.5 8.3

Velocity in horizontal pipe (ft/s) 2.3 4.7 4.7 9.0 9.5 9.2

Velocity in 2nd stack (ft/s) 7.2 7.3 7.9 8.1 8.9 8.1

Pressure in 1st stack (in. W.C.) -0.3 -10.5 -31.5 -40.1 -41.3 -40.1

Pressure in horizontal pipe (in. W.C.) -1.5 -11.2 -41.4 -40.4 -42.6 -43.4

Pressure in 2nd stack (in. W.C.) -2.6 -22.4 -43.8 -42.9 -43.8 -44.1




Water head (inch) 1” 2” 3” 4” 5” 6”





Water head (inch) 1” 2” 3” 4” 5” 6”





Pressure in 1st stack (in. W.C.) 0.7 -0.1 -0.5 -0.7 -0.9 -1.4





Water head (inch) 1” 2” 3” 4” 5” 6”



Pressure in drain pipe (in. W.C.) 0.7 0.6 -0.1 -0.1 -0.3 -2.3


Water head (inch) 1” 2” 3” 4” 5” 6”





Pressure in 1st stack (in. W.C.) 0.7 -0.2 -0.8 -0.8 -0.8 -36.6






Water head (inch) 1” 2” 3” 4” 5” 6”





Water head (inch) 1” 2” 3” 4” 5” 6”





Pressure in 1st stack (in. W.C.) 0.8 0.7 0.5 -13.4 -27.8 -22.2

Pressure in horizontal pipe (in. W.C.) 0.3 -0.4 -2.1 -15.0 -33.3 -45.1

Pressure in 2nd stack (in. W.C.) 0.4 -0.3 -5.0 -4.3 -49.8 -50.3


1. ManuFaCtuReR a, MoDel a-1

2” Cast iRon DRain with Cast iRon DoMe

DRain without DRain PiPe

water head (inch) 1” 2” 3” 4” 5” 6”


Velocity of flow (ft/s) 2.8 4.5 4.8 5.1 5.2 5.4

DRain with 10-Ft PiPe

water head (inch) 1” 2” 3” 4” 5” 6”


velocity in drain pipe (ft/s) 8.7 9.0 9.0 9.0 9.0 9.0

Pressure in drain pipe (in. w.C.) -3.8 -40.1 -55.1 -56.8 -55.0 -54.4


water head (inch) 1” 2” 3” 4” 5” 6”


velocity in 1st stack (ft/s) 3.9 7.8 7.9 8.0 8.2 8.3

velocity in horizontal pipe (ft/s) 3.8 8.7 8.7 8.7 8.8 8.7

velocity in 2nd stack (ft/s) 8.3 8.6 8.7 8.7 8.8 8.7

Pressure in 1st stack (in. w.C.) -1.4 -22.4 -21.0 -20.6 -19.0 -19.4

Pressure in horizontal pipe (in. w.C.) -3.0 -43.8 -45.5 -43.5 -44.6 -45.0

Pressure in 2nd stack (in. w.C.) -5.9 -43.7 -45.0 -45.0 -46.2 -45.2




water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”












water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”





Pressure in 1st stack (in. w.C.) 0.4 0.1 -2.4 -2.8 -4.3 -5.5






water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”





Pressure in 1st stack (in. w.C.) 0.9 -2.3 -18.9 -34.8 -34.4 -29.4







water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”



Pressure in drain pipe (in. w.C.) 0.8 -0.1 -28.9 -50.4 -50.8 -50.2


water head (inch) 1” 2” 3” 4” 5” 6”






Pressure in horizontal pipe (in. w.C.) 0.1 -0.5 -28.8 -72.1 -73.7 -76.0

Pressure in 2nd stack (in. w.C.) 0.8 -1.1 -42.4 -52.6 -52.5 -53.9

6. ManuFaCtuReR B, MoDel B-1



water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”












water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”











water head (inch) 1” 2” 3” 4” 5” 6”


Velocity of flow (ft/s) 1.5 2.8 4.1 4.3 5.3 6


water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”












water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”



Pressure in drain pipe (in. w.C.) 0.9 1.2 -1.8 -8.7 -20.2 -31.4


water head (inch) 1” 2” 3” 4” 5” 6”





Pressure in 1st stack (in. w.C.) 0.8 1.2 0.7 -5.4 -24.7 -29.1

Pressure in horizontal pipe (in. w.C.) 0.1 3.9 -6.9 -8.3 -34.8 -51.6


10. ManuFaCtuReR C, MoDel C-1

2” Cast iRon DRain with Poly DoMe


water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”












water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”











water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”












water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”











water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”



Pressure in drain pipe (in. w.C.) 2.7 3.4 2.8 -9.8 -30.9 -38.1


water head (inch) 1” 2” 3” 4” 5” 6”









15. ManuFaCtuReR D, MoDel D-1

2” Cast iRon DRain with aluMinuM DoMe


water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”











water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”












water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”





Pressure in 1st stack (in. w.C.) 1.1 0.4 0.9 0.7 -32.3 -33.6






water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”







Pressure in 2nd stack (in. w.C.) 1.2 1.0 -0.6 -9.2 -16.0 -44.4


19. ManuFaCtuReR e, MoDel e-1

2” PvC DRain with Poly DoMe


water head (inch) 1” 2” 3” 4” 5” 6” 7”

Flow of water into box (gpm) * 45 58 78 95 99 103

Velocity of flow (ft/s) * 2.8 3.7 3.9 4.0 4.1 4.4


water head (inch) 1” 2” 3” 4” 5” 6”


velocity in drain pipe (ft/s) * 8.1 9.0 9.0 9.0 9.0 9.0

Pressure in drain pipe (in. w.C.) * -2.2 -23.1 -24.3 -26.7 -27.9 -29.0


water head (inch) 1” 2” 3” 4” 5” 6”


velocity in 1st stack (ft/s) * 4.7 7.2 7.8 8.0 8.0 8.1

velocity in horizontal pipe (ft/s) * 4.4 7.5 8.6 7.8 7.8 8.9

velocity in 2nd stack (ft/s) * 7.9 7.8 8.5 8.9 8.7 8.7

Pressure in 1st stack (in. w.C.) * -3.1 -14.6 -21.9 -20.2 -18.3 -18.9

Pressure in horizontal pipe (in. w.C.) * -4.8 -29.3 -44.8 -44.6 -44.7 -45.5

Pressure in 2nd stack (in. w.C.) * -14.9 -20.4 -28.2 -25.5 -25.8 -30.4

* Water flows were too small for the sensors to read.




water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”






Pressure in horizontal pipe (in. w.C.) -0.1 -0.1 0.9 -6.3 -38.8 -61.4




4” PvC DRain with aluMinuM DoMe


water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”









6” PvC DRain with aluMinuM DoMe


water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”



Pressure in drain pipe (in. w.C.) 1.7 1.8 2.4 2.0 -2.8 -18.3


water head (inch) 1” 2” 3” 4” 5” 6”







Pressure in 2nd stack (in. w.C.) 0.9 0.8 0.8 -4.4 -10.6 -27.6





water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”



Pressure in drain pipe (in. w.C.) 0.1 0.3 -4.9 0.6 0.5 38.6


water head (inch) 1” 2” 3” 4” 5” 6”





Pressure in 1st stack (in. w.C.) 0.6 0.5 -1.3 0.1 -22.9 -34.7

Pressure in horizontal pipe (in. w.C.) 0.2 0.4 0.6 -1.6 -44.8 -59.4





water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”












water head (inch) 1” 2” 3” 4” 5” 6”


Velocity of flow (ft/s) 1 3.5 4.5 3.8 5.3 5.6


water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”





Pressure in 1st stack (in. w.C.) 0.8 -3.6 0.5 -4.0 -31.7 -32.2






water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”









27. ManuFaCtuReR F, MoDel F-1



water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”











water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”












water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”











water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”



Pressure in drain pipe (in. w.C.) 7.4 7.6 6.9 5.5 5.3 5.6


water head (inch) 1” 2” 3” 4” 5” 6”





Pressure in 1st stack (in. w.C.) 15.5 17.6 17.3 18.1 14.2 -5.4







water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”






Pressure in hor. pipe (in. w.C.) -1.6 -14.6 -37.2 -38.7 -48.5 -47.5





water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”






Pressure in hor. pipe (in. w.C.) 0.3 -5.2 -29.1 -56.4 -61.3 -61.2






water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”











water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”









35. ManuFaCtuReR g, MoDel g-1

2” PvC DRain with aBs DoMe


water head (inch) 1” 2” 3” 4” 5” 6”


Velocity of flow (ft/s) 1.2* 4.3 4.7 4.8 4.3 4.6


water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”








* Water flow was too small for the sensor to read consistently. This was an approximate number.




water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”












water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”











water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”





Pressure in 1st stack (in. w.C.) 0.7 -0.3 3.9 5.8 -1.3 -18.1




39. ManuFaCtuReR h, MoDel h-1



water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”


velocity in drain pipe (ft/s) 0.8* 9.0 8.6 9.0 9.0 9.0



water head (inch) 1” 2” 3” 4” 5” 6”








* Water flows were too small for the sensor to read consistently. These are approximate numbers.




water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”












water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”











water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”












water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”








44. ManuFaCtuReR i, MoDel i-1



water head (inch) 1” 2” 3” 4” 5” 6”

Flow of water into box (gpm) * 38 65 75 67 66

Velocity of flow (ft/s) * 2.2 3.7 3.0 3.5 4.1


water head (inch) 1” 2” 3” 4” 5” 6” 7”


velocity in drain pipe (ft/s) * 8.1 9.0 9.0 9.0 9.0 9.0

Pressure in drain pipe (in. w.C.) * -1.2 -16.8 -37.4 -50.1 -50.9 -51.8


water head (inch) 1” 2” 3” 4” 5” 6” 7”


velocity in 1st stack (ft/s) * 4.1 6.3 4.7 5.6 5.1 5.1

velocity in horizontal pipe (ft/s) * 3.5 5.2 5.2 6.0 5.4 5.8

velocity in 2nd stack (ft/s) * 8.5 7.8 7.2 7.1 7.3 7.2

Pressure in 1st stack (in. w.C.) * -1.8 -6.2 -1.2 -3.7 -1.3 -2.8

Pressure in hor. pipe (in. w.C.) * -5.8 -9.0 -7.9 -11.0 -10.0 -4.5

Pressure in 2nd stack (in. w.C.) * -9.8 -14.5 -12.5 -16.8 -17.5 -23.7

* Water flows were too small for sensor to read.





water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”











water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”






Pressure in hor. pipe (in. w.C.) 0.1 0.1 1.7 -1.7 -38.2 -59.3



47. ManuFaCtuReR J, MoDel J-1



water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”











water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”












water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”



Pressure in drain pipe (in. w.C.) 0.1 -0.2 -3.4 0.2 -25.2 -33.9


water head (inch) 1” 2” 3” 4” 5” 6”











water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”












water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”









2” Cast iRon DRain with BRass DoMe


water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”







Pressure in 2nd stack (in. w.C.) -1.8 -41.6 46.2 -39.2 -45.4 -45.8

* Note: Water flow was too small for the sensor to read consistently. This was an approximate number.





water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”











water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”












water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”



Pressure in drain pipe (in. w.C.) 1.8 1.7 -1.6 0.3 -17.6 -26.4


water head (inch) 1” 2” 3” 4” 5” 6”











water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”












water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”











water head (inch) 1” 2” 3” 4” 5” 6”




water head (inch) 1” 2” 3” 4” 5” 6”





water head (inch) 1” 2” 3” 4” 5” 6”








Storm Drainage System Research Project - IAPMO … ASPE Research Foundation Storm Drainage System...

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Transcript of Storm Drainage System Research Project - IAPMO … ASPE Research Foundation Storm Drainage System...